This invention is in the field of multi-section booms, such as telescoping booms and articulated booms and component sections of such booms, and is particularly directed to a unique articulated boom structure providing safe, reliable support and dielectric isolation for a personnel supporting basket at the outer end of the boom.
Utility companies, outdoor advertising companies and other companies having operations requiring the positioning of workmen or other personnel at elevated levels for installation, servicing or repairing of equipment frequently employ maintenance trucks on which power operated boom members having personnel supporting baskets at their outer ends are mounted. Normally, the inner end of such boom members is mounted for rotational movement about a vertical axis by a supporting pedestal or the like and is also mounted for pivotal movement about a horizontal axis on the pedestal. In many instances, the boom members are dimensioned and shaped to have adequate structural strength and capacity to enable support by the boom of relatively heavy auxiliary equipment such as ground drilling auger means for drilling pole holes or the like. Additionally, it is important that boom members employed by electrical companies and others for use in areas in close proximity to high voltage equipment employ a dielectric section electrically isolating the outer boom end and personnel supporting basket from the remainder of the structure in order to minimize the extremely dangerous possibility of creating a short circuit through the boom to the ground should any part of the outer boom portion accidentally contact a high voltage conductor.
It is desirable that boom members be dimensioned and constructed so as to permit the outer end of the boom to be easily positionable throughout a work area of substanial extent without repositioning of the boom supporting vehicle. It is also obviously imperative that such boom members have sufficient strength and structural integrity as to provide a substantial safety factor for the users.
Previous boom constructions have frequently employed a telescopic type construction in which two or more relatively axially movable boom members are mounted for extensible movement of the outer boom member outwardly from within the inner boom members. Other prior known constructions have disclosed articulated boom members in which the outer boom portion, which may or may not comprise a telescopic boom section, is pivotally connected to the outer end of an inner boom member which is pivotally supported on a pedestal in the well-known manner previously discussed.
All workmen supporting boom members must have adequate strength to safely support the weight of the workmen and associated equipment being employed by the workmen as well as having adequate strength to resist lateral and vertical inertia forces created by the stopping and starting of the boom movement during a positioning operation. It is desirable that a boom provide adequate resistance to stress conditions resulting from bending, buckling, shear forces and combination forces while providing such adequate resistance without employing excessively heavy and consequently cumbersome structural members. It is also desirable that boom members occupy a minimum amount of space when contracted on the supporting vehicle for transport from one job site to another.
Unfortunately, boom designs providing advantages in one area frequently suffer a consequent loss of a desirable characteristic in another area and an optimum boom design must consequently reflect a proper relative proportioning of conflicting design factors.
Therefore, it is the primary object of this invention to provide a new and improved boom construction having optimum functional characteristics.
A more specific object of the invention is the provision of a new and improved articulated boom construction.
Yet another object of the invention is the provision of a new and improved boom construction having design simplicity enabling achievement of economy both in fabrication and maintenance of the boom member.
A still further object of the invention is the provision of a new and improved boom construction having an improved strength to weight ratio.
Another object of the invention is the provision of a new and improved boom component usable either alone or as part of a compound boom structure.
Yet another object of the invention is the provision of a new and improved articulated boom construction having no internal parts requiring maintenance or servicing.
Achievement of the foregoing objects is enabled by the preferred embodiment of the invention as embodied in an articulated boom consisting of an inner steel boom member and an outer fiberglass boom member each of which is of unique design.
The inner boom is supported on its lower or inner end by a pivotal connection to a horizontal pivot shaft on a conventional support pedestal. The inner boom is formed of a hollow steel shell member of modified trapezoidal cross-section consisting, when considering the longitudinal axis of the inner boom positioned substantially horizontally, of a top web, a bottom web and first and second side webs joined along their lower edge portion by the bottom web to corresponding edge portions of the companion side webs. The first and second side webs are inclined in downwardly convergent relation with respect to a vertical plane passing through the axis of the inner boom member so that their edges connected to the bottom web are more closely spaced with respect to each other than are their edge portions connected to the top web. The side webs are symmetrical with respect to the vertical plane and the bottom web is arcuately curved about a center of curvature positioned within the interior of the hollow boom member.
A horizontal pivot pin mounted near the outer end of the inner boom member provides pivotal support for a steel elbow connector means including a boom support stub member extending outwardly from the pivot shaft. Support for the outer boom member is provided by the boom support stub member by virtue of the fact that the inner end of the outer boom member comprises a hollow coupling portion fitting over the stub member. In the preferred embodiment, the coupling portion is formed on the stub member during the fabrication of the entire boom on a mandrel on which the stub member is mounted. In an alternate mode of fabrication, the entire outer boom is fabricated by conventional procedures and the coupling portion is secured to the stub member by epoxy or other suitable adhesive or by mechanical securing means. The remaining portions of the outer boom member include a top wall, side wall and a bottom connector wall portion.
The top wall tapers inwardly from the inner to outer end of the outer boom and side walls taper inwardly from top to bottom with the amount of taper decreasing from the inner end to the outer end of the boom member so that the side walls at the outer end of the boom are in parallel relation with respect to each other. The bottom wall of the outer boom member is of arcuate, downwardly convex configuration having a center of curvature interiorly of the boom.
The prior known boom constructions have largely been of either rectangular cross-section or of circular cross-section, or of upwardly convergent trapezoidal configuration formed of metal truss members, insofar as the main boom elements are concerned. The boom of the present invention has been fully developed to provide an optimum cross-sectional configuration of the boom elements which provides substantial strength and weight advantages as compared to the prior known boom configurations.
In addition, the preferred embodiment employs a hydraulic cylinder mounted between the outer end of the inner boom member and the elbow connector in a space-saving manner for enabling a pivoting of the boom members with respect to each other.
Prior known fiberglass booms of rectangular cross-section have frequently employed an inefficient excessive amount of material due to the fact that they are designed with a very high safety factor insofar as resistance to bending stresses is concerned. It has been found that a substantially more efficient use of material can be achieved by the present invention which is based upon the provision of an appropriate shape for providing a properly balanced resistance to all stresses in an efficient manner.
Analysis of boom members having different geometric shapes and lengths established the substantial advantages of the present invention over the prior known boom constructions.
A better understanding of the manner in which the preferred embodiment achieves the foregoing objects and results will be enabled when the following written description is considered in conjunction with the appended drawings.